A prior art scroll pump 100 is shown in FIG. 3, and comprises a housing 102, a drive shaft 103 having a concentric shaft portion 104 and an eccentric shaft portion 106. The shaft is supported at its concentric portion by bearing means 108, which is fixed relative to housing 102, and is driven by a motor 110 which is mounted in the housing. A second bearing means 112 supports an orbiting scroll 114 on the eccentric shaft portion 106 so that during use rotation of said shaft imparts an orbiting motion to said orbiting scroll 114 which co-operates with a second, fixed, scroll 116 for pumping fluid along a fluid flow path 117 between an inlet and outlet of the pump. The radial clearances between the orbiting and fixed scrolls are accurately controlled so that lubricant is generally not required for scaling. The axial clearances between the scrolls are sealed with tip seals 118. The arrangement means that a scroll pump may be used when it is desired to maintain a dry environment for the pumping media along the fluid flow path. A bellows arrangement 120 isolates the first bearing means and the second bearing means from the fluid flow path, thereby restricting contamination of the pumping media, since the bearing means are generally lubricated. O-ring seals 121 and 122 are disposed between the bellows arrangement and orbiting scroll 114 and housing 102, respectively, to resist the passage of contaminants. The bellows arrangement is sufficiently flexible to allow orbiting motion of the orbiting scroll 114, second bearing means 112 and eccentric shaft portion 106. A counter-weight 123 is provided for balancing the weight of the orbiting components of the pump. The counter-weight is adapted to be fitted about the concentric shaft portion 104 of the drive shaft 103 radially between a flexible portion of the bellows arrangement 120 and the drive shaft 103.
During assemble, shaft 103, bearing means 108 and motor 110 are mounted relative to the housing 102. Counter-weight 123 is fitted onto the drive shaft 103 and fastened with a radially extending fastener of pin 125. Second bearing means 112 is then fixed to a hub 124 of orbiting scroll 114 with fasteners 126 (only one is shown). A flange 128 of the bellows arrangement is then fixed to the orbiting scroll with fasteners 129 (only one is shown). The orbiting scroll 114, second bearing means 112 and bellows arrangement 120 are then inserted together into the housing in the direction shown by arrow A. This assembly step involves passing the flexible portion of the bellows arrangement over the counter-weight, which is relatively awkward to achieve. When is position, flange 130 of bellows arrangement 120 is fastened to the housing by fasteners 132 (only one is shown). The fastening of fastener 132 is a difficult procedure since access to the fastener is through the relatively small gap G between the orbiting scroll 114 and the housing 102. It will be appreciated that insertion of a tool through gap G whilst also maintaining line of sight of fastener 132 is cumbersome and intricate. Once the tool is inserted through gap G there remains the difficulty of passing the bellows arrangement the latter of which has been expanded radially outwardly by the counter-weight 123.
Subsequently, fixed scroll 116 is fixed relative to the housing with fasteners 134 (only one is shown).
It is desirable to provide an improved scroll pump and method of assembling a scroll pump.